Method of increasing stress corrosion resistance of aluminum alloys



Unite fates atent 12,865,796 IVIE'IHGD F INCREASING STRESS CORROSION IRESISTANCE 0F ALUUM-ALLOYS Wilhelm RosenkranyMeinei-zhagen inWestphalia, Eichholz, Germany No Drawing. Application October 11, 1956*Seri'al-No. 615,223

'lClaims priority, application Germany 0ct0ber12,.1955 is enin ci.sms-12.7

The present invention rel'ates'to a method of increasing the'corrosion'resistance of aluminum alloys, and more particularly, it relates :to amethod of producing shaped 'aluminumalloy bodies having high corrosionresistance under conditions of stress.

The self-hardening properties of aluminum alloyscont'aining about 4% ofcopper and between 0.5 and 1% of magnesium are well'knowmandaluminum'alloys of the above composition have for many years played anim portantpart in the production of workpieces formed by non cutting'shapingysuch' as -aluminum 'alloy sheets, ex- 'trusions, forgingsandfthe like. However, it "became "soonapparent'thatthe above mentionedalloys are, due to their high 'copper'content; of less corrosionresistance ithen 'other' aluminum alloys. Especiallyin the "case 'ofaluminum alloy sheets of the above composition it 'hasbeen'fattempted'toovercome the'disadvantage of low corrosionresistancegby platingthe alloy sheet -with a V 'corrosion resistant,copper-free aluminum alloy, or, preferably, with-pure aluminum. -Therebyit could not-be 'avoided'that the strength-'of 'the-sheet or the likewasreduced in proportionto' thethickness or the plating layer.

It has then been triedto utilize copperfree aluminum alloys containingabout between 4% and 12% Zinc and about between 1% and 6% magnesium.Such aluminum alloys possess improved strength properties as comparedwith aluminum alloys of the aluminum-copper-magnesium type. However, itwas soon found out that the aluminumzinc-magnesium alloys were subjectto crack formation When'being exposed simultaneously to mechanicalstress and corrosive conditions. In other words,- aluminum alloys of thetype aluminum-zinc-magnesium showlow resistance against stresscorrosion, and for this reason-such alloys could not be used to thedesired extent in light metal construction forpurposes for which thesealloys, due to 'their'great strength properties, would otherwise havebeen highly suitable.

"The resistance of aluminum-zinc-magnesium alloys against stresscorrosion was then improved by including elements such as chromium,vanadium or manganese in the alloy, which elements were supposed toprevent or at least considerably reduce the susceptibility againststress corrosion of workpieces formed of the last mentioned alloys bynon-cutting shaping.

. 'As is described in greater detail in my copending application SerialNumber 560,890, now Patent 2,823,994, issued February 18, 1958, entitledAluminum Alloy and Workpiec'e, the customary testing .for susceptibilityto stress corrosion by means'of the so-called fork-test does not giveresults which correspond to the effects of stress under corrosiveconditions in the actual use of'structural elements and other bodiesobtained-from aluminum alloys by non-cutting shaping.

Discrepancies between test results and actual performance can beeliminated by a testing method combining bent tests with exposure toatmospheric conditions. In carrying. out=this improved test method,T-profiles of the various aluminum alloys which are produced withextrusion presses, .are .bent in the plane of the T iiang'e about thestem and then exposed to real or siniulat'ed atmospheric conditions.After more or. less -1prolonged testing periods, the workpiece isexamined forthe .ap-

.pearance of the typical stress corrosion-cracks which usually areformed injthe once .upset areasof the T-profile stem.

The results obtained in accordance with this improved testing methodclearly show that even aluminumiincmagnesium alloys whichhave beenstabilized with chromium, vanadium or manganese are ,far interior withrespect to stress corrosionresistance, toaluminurn alloys of thealuminum-copp erfmagnesium type. A f y d clos dii my c nt n n pplica,seria Number 9 n '-P n .2 ,;9 4 issue f ebruary '18, 1958, abovereferred to, it has been jtoundthat great resistance against stresscorrosion.canbe achieved by including a small percentage of silver inthe aluminumzinc-magnesium type alloy' which also contains aismallquantity of chromium and/ or manganese and/or vanadium. "However, theaddition of .silver to the aluminum alloy is frequently undesirable,primarily because ofthe relatively high costs-thereof. It must be notedhowever, that excellent results havebeen obtained by subjec ting asilver-containing aluminum alloy of j the type described above to themethod ofthe present invention as described further below.

It-is an object of the present invention to overcome the above describeddifficulties in the production of yhigh strength;stress-corrosionresistant aluminum alloy workpieces.

-'It is anotherobject of the' presentinvention to provide a method ofproducing shaped aluminum alloy bodies "of high-stress corrosionresistance consisting of an aluminu'm alloy of thealuminum-Zinc-magnesium type.

It is 'yet'another object of=the-present inventionto increasethecOrrosion resistance under-stress of shaped aluminum alloy bodies inan economical and easily controllable manner by suitably adjusting thetemperature of the aluminum alloy body duri-ng the variousheattreatments thereof.

- With the above and'zother o'bjectsin view, the'present inventionmainly comprises in a method of producing shaped aluminum alloy bodieshaving high corrosion 're sistance under conditions of stress, thestepsof annealing an aluminum alloybody consisting essentially :ofaluminum and; between 4% and 12% -of zinc, between --1% and':6% ofmagnesium; at least one metal belonging to the group consisting ofchromium, vanadium and .man- =ganese,in-amounts of between 0.05 and 0.6%chromium,i'0.'05% and 0.15% vanadium -and'0;l% to 1 .5 manganese, at afirst temperature :and for a period :of .time sufiicient to causesubstantially equalization of concentration:Qf-themagnesiumand-of thezinc within the crystallites iof. theialuminum: alloy body, the firsttemperature being so chosen as to maintain substantially the one metalin. solution within the alloy: thereby preventing precipitation thereofin.the forrn=of an intermetallic compound, and maintainingv the aluminumalloy body during subsequent nonacutting shaping thereof; at a.temperature adapted to retain substantially :the one, metal-insolutionin the' alloy, whereby a shapedqaluminum alloybody of great stresscorrosion resistance is, formed.

'In a;pref er red manner of carrying out the method; of the; presentinvention, the same comprises the steps of annealing an aluminum alloybody consisting essential- .ly of aluminum and between 4% and 12%, ofzinc, .be- .tween 1%, and 6% ofrnagnesium, at least one metal belongingto the groupconsisting of chromium, vanadium and manganese,,in amountsofbetween 0.05% and 0.6% chromium, 0.05% and 0.l5%,vanadium and 0.1% to1.5% ;manganese,.. t a, first temperature andsf or ape.-

Pa en e a a rind of time sufficient to cause substantially equalizationof concentration of the magnesium and of the zinc within thecrystallites of the aluminum alloy body, the first temperature being sochosen as to maintain substantial- 1y 1 theone' metal in solution withinthe alloy thereby preventing precipitation thereof in the form of anintermetallic compound, adjusting the temperature of the aluminum alloybody to a second temperature sutliciently high to allow non-cuttingshaping of the alloy body and not more than 20 C., higher than the firsttemperature, subjecting the aluminum alloy body to noncutting shapingwhile the same is substantially at the second temperature, subjectingthe thus shaped aluminum alloy body to solution heat treatment at a.temperature not exceeding the first temperature by more than 50 C.,quenching the heat treated shaped aluminum alloy body at roomtemperature, and subsequently hardening the same in boiling water,whereby a shaped aluminum alloy body of great stress corrosion Ileastone of the stabilizing elements chromium, vanadium and manganese inan amount of between 0.05% and 0.6%, preferably in an amount of between0.15% and 0.25% chromium, 0.05% and 0.15% vanadium and 0.1% to 1.5%manganese. Most preferably the amount of manganese in the alloy is keptat about 0.8%, and the alloy may also contain in addition to theaforementioned essential constituents thereof, up to 2% copper and/ orup to 1% silver plus the amounts of iron and silicon which are usuallypresent as impurities in commercial aluminum.

When the resistance against stress corrosion of the above describedalloys of the aluminum-zinc-magnesium type is tested by extruding thesame in the shape of T- profiles, then bending in the plane of theT-flange about the stem and exposing to atmospheric conditions, it isfound that typical stress corrosion cracks usually occur, while suchstress corrosion cracks do not occur upon similar treatment of the lowerstrength alloys of the aluminum-copper-magnesium type.

It is well known that aluminum alloys are susceptible to stresscorrosion only along the grain-boundaries which, in the case ofaluminum-zinc-rnagnesium alloys in contrast to aluminum-copper-magnesiumalloys, are electrochemically less noble than the mixed crystal. In viewthereof it has now been attempted to produce workpieces ofaluminum-zinc-magnesium alloys by noncutting shaping in such a manner,i. e. with such a structure, that the corrosive attack is diverted fromthe grain boundaries. This can be achieved by forming in thecrystallites structural constituents which are less noble then the grainboundaries.

Surprisingly it has been found that this can be achieved, according tothe present invention by maintaining during heat treatment andnon-cutting shaping of the aluminum alloy of the aluminum-zinc-magnesiumtype, which alloy also contains a small quantity of a stabilizer such aschromium, vanadium, manganese or another metal performing a similarfunction, definite temperature ranges as described further below.

The term stabilizer as used in the present application is meant todenote any one of the metals chromium, vanadium, manganese or of othermetals performing the same function as the aforementioned metals withinthe alloy, or any combination of several of these metals.

It is essential in accordance with the present invention that theannealing or heat treatment of the aluminum alloy body prior tonon-cutting shaping thereof iscarried out at a temperature above thesolubility temperature of the respective alloy, which temperaturedepends upon the contents of magnesium and zinc,'as is well known withthe skill of the art, which temperature must also be such thatsubstantially equalization of the concentration of the hardening alloycomponents zinc and magnesium takes place within the crystallites of thealuminum alloy body, while precipitation of the stabilizer metal whichis present in a meta-stable solution, in the form of an intermetalliccompound is prevented as far as possible. The thus achieved structuralcondition with respect to the stabilizer metal must then be maintainedduring transformation of the original aluminum alloy body or ingot intoa shaped aluminum alloy body and also during heat hardening of theshaped body. Consequently, according to the present invention, theheating of the ingot which has previously been heat treated as describedabove, prior to deformation thereof, for instance by means of anextrusion press, must be carried out at a temperature which does notexceed the temperature of the previous heat treatment by more than 20 C.In order to prevent the precipitation of stabilizer metal-containing,for instance chromium-containing, compounds it has been foundadvantageous according to the present invention to carry out the secondor predeformation heating ofthe aluminum alloy body by induction heatingfor a short period of time. The solution heat treatment of the shapedaluminum alloy body in a salt bath or the like must also be carried outat a temperature and for a period of time which will not causeprecipitation of stabilizer metal-containing compounds. Consequently,according to the present invention, solution heat treatment is to becarried out at a temperature which at most exceeds the temperature ofthe pre-shaping first heat treatment by 50 C. The solution heattreatment too is preferably carried out for a relatively short period oftime only. Solution heat treatment of the shaped aluminum alloy body isthen followed in customary manner by quenching of the same at roomtemperature, preferably at about 15 C., and, finally, by hardening,preferably in boiling water. i. e. at a temperature of about 100 C.

By following the above described method of the present invention, apreviously unattainable degree of stress corrosion resistance, asmeasured by the improved test ing method described herein, is achieved.Optimum results are obtained when precipitation of stabilizermetalcontaining compounds is not at all or only to a slight degreeapparent in the finished shaped workpiece. How. ever, even when thetemperatures during the process of the present invention have not beencontrolled with sufficient accuracy so as to prevent precipitation ofchromium or other stabilizer metal-containing compounds to a markeddegree, the equalization of concentration of magnesium and zinc withinthe crystallites, and the reduction in the relative amount of thestabilizer metal which will precipitate, causes an improvement in thestress corrosion resistance of the workpiece, which, as stated above wasso far not attainable with alloys of similar composition.

The specific narrow temperature ranges which are to be maintainedaccording to the present invention in order to achieve highest stresscorrosion resistance of the finished shaped workpiece, i. e., thetemperature range for the heat treatment of annealing of the aluminumalloy ingots as well as the temperature range for the non-cuttingshaping thereof depend to a considerable degree on the specificcomposition of the aluminum alloy and can easily be ascertained bysimple tests which are well within the skill of the art.

The following examples are given as illustrative only of the method ofthe present invention, the present invention, however, not being limitedto the specific details of the examples.

Example 1 Aluminum alloy ingots of the composition 4.53% zinc, 3.54%magnesium, 0.18% copper, 0.41% chro- Aluminum alloy ingots of the samecomposition were,

similarly treated, with the exception that the 6 days preshapingannealing treatment was omitted.

The T-profiles obtained with and without the preshaping annealingtreatment were then tested for stress corrosion resistance according to'the above described improved method.

Thereby it was found that the life span of the T-profiles formed fromaluminum alloy ingots which had not been preheated varied in fivetestsbetween 4 and 53 days, while theI'F-profiles formed from aluminum alloyingots whichwere preheated=to460 C. as described abovewithstoodtestscontinuing for over 90 days.

Example 2 Comparisontests were carried out with an aluminum alloyhavingthe following composition: 4.20% zinc, 3.60% magnesium, 0.97% copper,0.20% chromium, 0.28% iron, 0.14% silicon and the balance aluminum. In;test (a) T-profiles were formed without preceding heattreatment. In test(b) the aluminum alloy ingots were first heated for a period of 3 daysto 450 C., and in test the aluminum alloy ingots were first heated for-aperiod of '3 days'to-510 C.

The ingot temperature during extrusion of the T-profiles-was kept in allexperiments at 420 C., solution heating was;carried out in all tests forminutes in a salt bath'of-450 6., and, also in all tests, the profileswere hardenedfor 100 hours in boiling water.

Thereafter, the T-profilesobtained in tests (a), (b) and-(c) wereexamined by etching surface portions thereof, using for the etching ofthe surface portions nitric acid plus mixed solution according to Dixand Keller, and by being. subjected to the improved method of testingfor stress corrosion bybending under atmospheric conditions.Thefollowing results were obtained:

Test Surface Etching Life .Span in Stress Corrosion Test (a)-.- SharpDistinct grainboundbetween 4 and 43 days.

' arias.- (b) grain boundaries not apunbroken after more: than parent.-100 days. (0) sharp distinct grainboundbetween 57 and 82 days.

anes.

. as in test (0), the cast structure is subjected to homogenizing heattreatment so as to equalize concentrations, where by all or part ofthe.chro-miurn. is precipitated in the form of an intermetalliccompound, the tendency towards re crystallization is .also greatly.increased, so that in similar mannerstress corrosion effects becomeapparent.

Example 3 Tests were; carried out as more fully describedin Example 2,however, with-an aluminum alloy of the fol-, lowing,difierentcomposition: 4.09% zinc, 3.61% mag.- nesium,,0. l0% copper,1.12%'manganese, 0.28% iron, 0.07% silicon and thebalance aluminum.

h.e,.- fe p n he z -rw le p qd c dsi m 6 above-described alloyundertheconditions; describediint Example 2 was as follows:- 1

Test

5, 3, 5, 5 days. :unbroken after more thanlOO days;

5, 6, 4, 5 days.

Example 4 Tests carried out according to Example- Z'With-an' aluminumalloy of the composition: 4.19% zinc; 3;78%i; magnesium, 1.49% copper,0.52%v manganese, 0.24% iron, 0.12% silicon and the balance aluminum,gave? results similar to those'described in Example 3'.

Example 5 An aluminum alloycontaining large: percentage: amounts ofalloying materialssuch as: 9.38% zinc, 2.07%? magnesium, 0.16% copper,0.32% chromium, 0.24%. iron, 0.10% silicon and the balance aluminum, hashigh strength characteristics (0 :65-66 kg./mm. a0'.2=60: 62 kg/mmfi, a=5%, H =185 kg./mm.'

T-profiles were produced from the above alloy according to the method ofthe present invention by first heating 1 the ingots for a period ofthree days to a temperature of 430 C., extruding the profiles at analloy temperature of 440 C, subjecting the extruded T-profiles tosolutionheat treatment for a period of '15 minutes in a-salt bath havinga temperature of 450 C, quenching at about 15 C., and subsequentlyhardening. for hours in boiling water.

The thus produced T-profiles were still unbroken after being tested formore than 100 days according to the improved method of testing stresscorrosion resistance, while the life span of T-profiles produced fromthe same alloy and tested under the same conditions, but without thepre-shaping annealing treatment, or with pre-shaping homogenizing heattreatment at temperatures exceedingthe permissible temperaturesaccording to the present invention, showed varying shorter life spans,some as short" as 6 days.

Example- 6 mediately prior to non-cutting deformation, the-ingots wereheated inductively fora short period of time-to 430;

C. Thereafter T -profiles were formed on .an-extrusion press of theheated ingots. TheT profiles-were then solution heated at 450 C. in asaltbath for 15 minutes; quenched in water of room temperature, andsubsequent- 1y hardened for 100 hours in boiling water.

Bend testing under atmospheric conditions according to the improvedmethod for determining,stress corrosion resistance, showed that thelifespan of thebent portions of the T-profiles exceeded 100 days.

The structure of shaped aluminum'bodies produced according to thepresent invention .shoWs aftersolution heating'and subsequent quenchinga typical reticulated and line forming pattern. This recticularstructure. is. characteristic for the deformed,. but not recrystallizedsupersaturated structural'condition. It isprobable that the boundarieswithin this reticular structure represent lattice-planes which weredisturbed due to deformation.

a protective eifect for the stresscorrosion endangered grain boundaries.In case of recrystallization, however, this reticular structuredisappears and consequently also its protective effect with respect tothe grain boundaries.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of the invention and,therefore, such adaptations should and are intended to be comprehendedwithin the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05% and 0.6% chromium, 0.05% and 0.15% vanadiumand 0.1% to 1.5% manganese, at a first temperature and for a period oftime sutficient to cause substantially equaliza tion of concentration ofsaid magnesium and of said zinc within the crystallites of said aluminumalloy body, said first temperature being so chosen as to maintainsubstantially said one metal in solution within said alloy and toprevent substantially precipitation thereof in the form of anintermetallic compound; and maintaining said aluminum alloy body duringsubsequent non-cutting shaping thereof at a temperature adapted toretain substantially said one metal in solution in said alloy, whereby ashaped aluminum alloy body of great stress corrosion resistance isformed.

2. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05% and 0.6% chromium, 0.05% and 0.15 vanadiumand 0.1% and 1.5% manganese, at a first temperature and for a period oftime sufiicient to cause substantially equalization of concentration ofsaid magnesium and of said zinc within the crystallites of said aluminumalloy body, said first temperature being so chosen as to maintainsubstantially said one metal in solution within said alloy and toprevent substantially precipitation thereof in the form of anintermetallic compound; and maintaining said aluminum alloy body duringsubsequent noucutting shaping and heat treatment thereof at atemperature adapted to retain substantially said one metal in solutionin said alloy, whereby a shaped aluminum alloy body of great stresscorrosion resistance is formed.

3. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05% and 0.6% chromium, 0.05% and 0.15% vanadiumand 0.1% to 1.5% manganese, at a first temperature and for a period oftime sufiicient to cause substantially equalization of concentration ofsaid magnesium and of said zinc within the crystallites of said aluminumalloy body, said first temperature being so chosen as to maintainsubstantially said one metal in solution within said alloy and toprevent substantially precipitation thereof in the form of anintermediate compound; adjusting the temperature of said aluminum alloybody to a second temperature sufiiciently high to allow non-cuttingshaping of said aluminum alloy body, to retain substantially said onemetal in Col solution in said alloy'and not more than 20 C. higher thansaid first temperature; subjecting said aluminum alloy body tonon-cutting shaping while the same is substantially at said secondtemperature; and subjecting the thusshaped aluminum alloy body tosolution heat treatment at a temperature not exceeding said firsttemperature by more than 50 C. and such as to prevent any substantialprecipitation of said one metal, whereby a shaped aluminum alloy body ofgreat stress corrosion resistance is formed. 7

4. in a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05% and 0.6% chromium, 0.05% and 0.15% vanadiumand 0.1% to 1.5 manganese, at a first temperature and for a period oftime sufiicient to cause substantially equalization of concentration ofsaid magnesium andof said zinc Within the crystallites of said aluminumalloy body, said first temperature being so chosen as to maintainsubstantially said one metal in solution Within said alloy and toprevent substantially precipitation thereof in the form of anintermediate compound; adjusting the temperature of said aluminum alloybody to a second temperature sufficiently high to allow non cuttingshaping of said aluminum alloy body, to retain substantially said onemetal in solution in said alloy and not more than 20 C. higher than saidfirst temperature; subjecting said aluminum alloy body to non-cuttingshaping while the same is substantially at said second temperature;subjecting the thus-shaped aluminum alloy body to solution heattreatment at a temperature not exceeding said first temperature by morethan 50 C. and such as to prevent any substantial precipitation of saidone metal; quenching said heat treated shaped aluminum alloy body atroom temperature; and subsequently hardening the same in a hardeningbath at about C., whereby a shaped aluminum alloy body of great stresscorrosion resistance is formed.

5. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05% and 0.6% chromium, 0.05% and 0.15% vanadiumand 0.1% to 1.5% manganese, at a first temperature and for a period oftime sufiicient to cause substantially equalization of concentration ofsaid magnesium and of said zinc within the crystallites of said aluminumalloy body, said first temperature being so chosen as to maintainsubstantially said one metal in solution within said alloy and toprevent substantially precipitation thereof in the form of anintermediate compound; adjusting the temperature of said aluminum alloybody to a second temperature sufiiciently high to allow non-cuttingshaping of said aluminum alloy body, to retain substantially said onemetal in solution in said alloy and not more than 20 C. higher than saidfirst temperature; subjecting'said aluminum alloy body to non-cuttingshaping while the same is substantially at said second temperature;subjecting the thus-shaped aluminum alloy body to solution heattreatment at a temperature not exceeding said first temperature by morethan 50 C. and such as to prevent any substantial precipitation of saidone metal; quenching said heat treated shaped aluminum alloy body atroom temperature; and subsequently hardening the same in boiling water,whereby a shaped aluminum alloy body of great stress corrosionresistance is formed.

6. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions ofstress, the; steps ofxannealingan aluminumalloy body.

consisting essentially of aluminum and. between 4% and 12% of zinc,between 1% anal 6% of magnesium, up to 1% of silver, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05 and 0.6% chromium, 0.05 and 0.15% vanadiumand 0.1% to 1.5% manganese, at a first temperature and for a period oftime suflicient to cause substantially equalization of concentration ofsaid magnesium and of said zinc Within the crystallites of said aluminumalloy body, said first temperature being so chosen as to maintainsubstantially said one metal in solution within said alloy and toprevent substantially precipitation thereof in the form of anintermetallic compound; and maintaining said aluminum alloy body duringsubse quent non-cutting shaping thereof at a temperatureadaptedtoretainsubstantially said one metal-in solution in said alloy,whereby a shaped aluminum alloy body of great stress corrosionresistance is formed.

7. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, up to 2% copper, atleast one metal belonging to the group consisting of chromium, vanadiumand manganese, in amounts of between 0.05% and 0.6% chromium, 0.05 and0.15% vanadium and 0.1% to 1.5% manganese, at a first temperature andfor a period of time sufiicient to cause substantially equalization ofconcentration of said magnesium and of said zinc within the crystallitesof said aluminum alloy body, said first temperature being so chosen asto maintain substantially said one metal in solution within said alloyand to prevent substantially precipitation thereof in the form of anintermetallic compound; and maintaining said aluminum alloy body duringsubsequent non-cutting shaping thereof at a temperature adapted toretain substantially said one metal in solution in said alloy, whereby ashaped aluminum alloy body of great stress corrosion resistance isformed.

8. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, up to 1% of silver, upto 2% of copper, at least one metal belonging to the group consisting ofchromium, vanadium and manganese, in amounts of between 0.05% and 0.6%chromium, 0.05% and 0.15% vanadium and 0.1% to 1.5% manganese, at afirst temperature and for a period of time sufficient to causesubstantially equalization of concentration of said magnesium and ofsaid zinc within the crystallites of said aluminum alloy body, saidfirst temperature being so chosen as to maintain substantially said onemetal in solution within said alloy and to prevent substantiallyprecipitation thereof in the form of an intermetallic compound; andmaintaining said aluminum alloy body during subsequent non-cuttingshaping thereof at a temperature adapted to retain substantially saidone metal in solution in said alloy, whereby a shaped aluminum alloybody of great stress corrosion resistance is formed.

9. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, and between 0.05 and1.5% of at least one stabilizer metal, at a first temperature and for aperiod of time sufficient to cause substantially equalization ofconcentration of said magnesium and of said zinc within the crystallitesof said aluminum alloy body, said first temperature being so chosen asto maintain substantially said one metal in solution within said alloyand to prevent substantially precipitation thereof in the form of anintermetallic compound; andmaintainingsaid aluminum alloybodysduringsubsequent non-cuttingishaping. thereof at a. temperaturei adapted-toretain substantially saidv one, metal in solution; in said alloy,whereby a shaped aluminum,alloyibody of':

great stress, corrosion resistance. is. formed.

10. In a method of-producing. shaped aluminum alloy' bodies having, highcorrosion resistance under conditions,

of .stress, the stepsof annealing an aluminum alloybody a; period oftimesufiicient to causesubstantially equalizaa tion of concentration ofsaidmagnesium and-:of said zinc. within the crystallites of saidaluminumiallo-y.body,.said:

first temperature being so chosen as to maintain substantially said onemetal in solution within said alloy and to prevent substantiallyprecipitation thereof in the form of an intermetallic compound; andadjusting the temperature of said aluminum alloy body prior tonon-cutting shaping thereof for a short period of time to a temperatureadapted to retain substantially said one metal in solution in said alloyand not exceeding said first temperature by more than 20 C.

11. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05% and 0.6% chromium, 0.05% and 0.15% vanadiumand 0.1% to 1.5 manganese, at a first temperature and for a period oftime sufiicient to cause substantially equalization of concentration ofsaid magnesium and of said zinc within the crystallites of said aluminumalloy body, said first temperature being so chosen as to maintainsubstantially said one metal in solution within said alloy and toprevent substantially precipitation thereof in the form of anintermetallic compound; adjusting the temperature of said aluminum alloybody to a second temperature sulficiently high to allow non-cuttingshaping of said aluminum alloy body, to retain substantially said onemetal in solution in said alloy and not more than 20 C. higher than saidfirst temperature; subjecting said aluminum alloy body to non-cuttingshaping while the same is substantially at said second temperature;subjecting the thus-shaped aluminum alloy body to solution heattreatment at a temperature not exceeding said first temperature by morethan 50 C. and such as to prevent any substantial precipitation of saidone metal; quenching said heat treated shaped aluminum alloy body at atemperature of about 15 C.; and subsequently hardening the same inboiling water.

12. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and between 4%and 12% of zinc, between 1% and 6% of magnesium, at least one metalbelonging to the group consisting of chromium, vanadium and manganese,in amounts of between 0.05% and 0.6% chromium, 0.05% and 0.15%

' vanadium and 0.1% to 1.5% manganese, the zinc content of said alloybeing greater than the magnesium content thereof, at a first temperatureand for a period of time sufiicient to cause substantially equalizationof concentration of said magnesium and of said zinc within thecrystallites of said aluminum alloy body, said first temperature beingso chosen as to maintain substantially said one metal in solution Withinsaid alloy and to prevent substantially precipitation thereof in theform of an intermetallic compound; and maintaining said aluminum alloybody during subsequent non-cutting shaping thereof at a temperatureadapted toretain s'ubstantially said one metal in solution in saidalloy,whereby a shaped aluminum alloy body of great stress corrosionresistance is formed.

13. In a method of producing shaped aluminum alloy bodies having highcorrosion resistance under conditions of stress, the steps of annealingan aluminum alloy body consisting essentially of aluminum and betweenabout 4% and 10% of zinc, between about 2% and 4% of magnesium, and atleast one metal belonging to the group consisting of chromium, vanadiumand manganese, in amounts-of'between 0.05% and 0.6% chromium, 0.05% and0.15% vanadium and 0.1% to 1.5% manganese, at a first temperature andfor a period of time suificient to cause substantially equalization ofconcentration of said magnesium and of said zinc within the crystallitesof said aluminum alloy body, said first temperature being so chosen asto maintain substantially said one'metal References Cited in the file ofthis patent UNITED STATES PATENTS 2,165,441 Beck et a1. July 11, 19392,736,674 Harmon Feb. 28, 1956 FOREIGN PATENTS 438,512 Great BritainNov. 11, 1935

5. IN A METHOD OF PRODUCING SHAPED ALUMINUM ALLOY BODIES HAVING HIGHCORROSION RESISTANCE UNDER CONDITIONS OF STRESS, THE STEPS OF ANNEALINGAN ALUMINUM ALLOY BODY CONSISTING ESSENTIALLY OF ALUMINUM AND BETWEEN 4%AND 12% OF ZINC, BETWEEN 1% AND 6% OF MAGNESIUM, AT LEAST ONE METALBELONGING TO THE GROUP CONSISTING OF CHROMOUM, VANADIUM AND MANGANESE,IN AMOUNTS OF BETWEEN 0.05% AND 0.6% CHROMIUM, 0.05% AND 0.15% VANADIUMAND 0.1% TO 1.5% MANGANESE, AT A FIRST TEMPERATURE AND FOR A PERIOD OFTIME SUFFICIENT TO CAUSE SUBSTANTIALLY EQUALIZATION OF CONCENTRATION OFSAID MAGNESIUM AND OF SAID ZINC WITHIN THE CRYSTALLITES OF SAID ALUMINUMALLOY BODY, SAID FIRST TEMPERATURE BEING SO CHOSEN AS TO MAINTAINSUBSTANTIALLY SAID ONE METAL IN SOLUTION WITHIN SAID ALLOY AND TOPREVENT SUBSTANTIALLY PRECIPITATION THEREOF IN THE FORM OF ANINTERMEDIATE COMPOUND; ADJUSTING THE TEMPERATURE OF SAID ALUMINUM ALLOYBODY TO A SECOND TEMPERATURE SUFFICIENTLY HIGH TO ALLOW NON-CUTTINGSHAPING OF SAID ALUMINUM ALLOY BODY, TO RETAIN SUBSTANTIALLY SAID ONEMETAL IN SOLUTION IN SAID ALLOY AND NOT MORE THAN 20*C. HIGHER THAN SAIDALLOY AND NOT JECTING SAID ALUMINUM ALLOY BODY TO NON-CUTTING SHAPINGWHILE THE SAME IS SUBSTANTIALLY AT SAID SECOND TEMPERATURE SUBJECTINGTHE THUS-SHAPED ALUMINUM ALLOY BODY TO SOLUTION HEAT TREATMENT AT ATEMPERATURE NOT EXCEEDING SAID FIRST TEMPERATURE BY MORE THAN 50*C. ANDSUCH AS TO PREVENT ANY SUBSTANTIAL PRECIPITATION OF SAID ONE METAL;QUECHING SAID HEAT TREATED SHAPED ALUMINUM ALLOY BODY AT ROOMTEMPERATURE; AND SUBSEQUENTLY HARDENING THE SAME IN BOILING WATER,WHEREBY A SHAPED ALUMINUM ALLOY BODY OF GREAT STRESS CORROSIONRESISTANCE IS FORMED.